As well known in the art, in an internal combustion engine (ICE), the combustion process and pollutant emissions are worst at engine start-up, when the ICE is still cold. In order to reduce the warm-up time necessary to make the internal combustion engine fully effective, i.e. in order to speed up the warm-up of the engine, is common technique to divert the coolant flowing in the cooling loop circuit back to the engine, without allowing the coolant to reach the relevant radiator, till the coolant temperature, and hence the engine, reaches a target temperature, that is around 90° C.
In this regard, a cooling circuit of an internal combustion engine comprises a circuit loop for the coolant (e.g. water), connecting the engine to the radiator, and a coolant pump. The cooling circuit is usually provided with a by-pass conduit to exclude the radiator, as well as with a thermostat that allows the coolant to divert back to internal combustion engine, and hence it prevents the coolant from flowing through the radiator, till the coolant temperature reaches said target temperature, that is generally about 90° C.
Such a thermostat, that is a three-way valve actuated by temperature, is usually a wax-type thermostat, in which a thermostat body comprises two inlets, coming from the engine via the by-pass conduit, and from the radiator respectively, and one outlet directed to the engine, as well as a closure element integral to a piston that is slidingly actuated by wax contained in a wax chamber, which in turn is thermally connected to the coolant flowing through the thermostat body.
In one example, the closure element of thermostats in a cooling system of an internal combustion engine opens or closes the pathway between the inlet from the radiator and the outlet to the engine, while usually the pathway between the inlet from engine and the outlet to engine remains always open.
The thermostat includes a return spring biasing the closure element towards its closing position and, since the piston integral to the closure element of the thermostat is mechanically linked to the wax in the wax chamber, when the wax increases its volume (due to the raising of the coolant temperature within the thermostat body) the piston is pushed by the same wax, in contrast to the spring action, to move the closure element until it reaches its opening position.
Usually wax is chosen in such a way that when the target temperature of the coolant is almost reached, it changes its status from solid to liquid, expanding its volume as well, and thus pushing the piston in contrast to the spring and opening the pathway between the radiator inlet and the engine outlet of the thermostat.
To improve the behavior of the thermostat, is well known to provide it with heating means, generally constituted by some electrical heater regulated by the ECU (Engine Control Unit) of the power-train, acting by heating the wax in said wax chamber.
The presence of an electrical heater for heating the wax even when the coolant has not yet reached the target temperature, thus opening the pathway between the radiator and the engine when the ECU decides it is appropriate, allows a more stable behavior of the thermostat as well as a quick cooling of the engine when the heat produced from this latter may cause overheating problems to the same engine.
Overheating problems may affect the wax contained in the wax chamber of the thermostat, as well, when the coolant temperature raises too much, thus causing the change of the wax state from solid to gas, which may damage the wax thermostat.
Such overheating problems affecting the wax in the wax chamber may also arise when the aforesaid heating means are actuated at the engine start-up in order to allow the engine cooling—i.e. to allow the coolant flowing through the radiator—even at low temperatures of the coolant.
In fact, in presence of certain external and/or internal thermodynamic conditions of the powertrain system, it may be useful to allow the coolant to flow through the radiator, thus cooling the internal combustion engine, even if the coolant temperature has not yet reached the aforesaid target temperature.
In this case, also due to the fact that said heating means are usually controlled by the ECU with an open loop control, said heating means may heat the wax in the wax chamber too much, which may damage the wax thermostat.
Thus, it may be desirable to provide a new wax-type thermostat for the cooling system of an internal combustion engine that does not show the problems described above, and hence that prevents damage to the wax thermostat. It may also be desirable to provide a wax-type thermostat that allows the release of more heat to the wax so that the opening of the thermostat can be anticipated, without the risk of damaging the wax thermostat. In addition, other objects, desirable features and characteristics will become apparent from the subsequent summary and detailed description, and the appended claims, taken in conjunction with the accompanying drawings and this background.